The role of C-centered radicals on the mechanism of action of artemisinin

Artemisinin is a sesquiterpene lactone with an endoperoxide function that is essential for its antimalarial activity. Endoperoxides are supposed to act on heme leading to the reduction of the peroxide bond and production of radicals, which can be responsible for killing the parasite. The geometries of artemisinin, radical anions and neutral species generated by rearrangement after reduction of the peroxide bond were fully optimized with the AM1 and PM3 semi-empirical methods, in order to characterize the intermediates formed during the process. Among the radicals calculated along the pathway for reductive decomposition of artemisinin, the secondary radical centered on carbon C₄ has the highest stability when compared to other radicals that can be achieved either by hydrogen migration to the original O-centered radical or by homolytic break of C–C bond. This suggests that the C₄-centered radical may be the species responsible for killing the parasite, as has been indicated previously in experimental studies.     

Simultaneous densitometric determination of artemisinin, artemisinic acid and arteannuin-B in Artemisia annua using reversed-phase thin layer chromatography

A rapid and simple RP-TLC method for simultaneous quantification of pharmacologically important sesquiterpene artemisinin (AM) together with its precursors arteannuin-B (AB) and artemisinic acid (AA) in the inflorescence part of Artemisia annua plant has been developed. The RP-TLC of sesquiterpenes was performed on RP-18 F254 S thin-layer chromatographic plates by developing in mobile phase, containing 0.2% TFA in water/ACN (35:65, v/v). The densitometric determination of AM, AB and AA was carried out after derivatization with anisaldehyde reagent at 426 nm in absorption-reflectance mode.     

A selective artemisinin-sensor using metalloporphyrin as a recognition element entrapped in the Au-nanoparticles-chitosan modified electrodes

An amperometric artemisinin (ARN) sensor based on the supramolecular recognition of glycosylated metalloporphyrin, which is included in the Au-nanoparticles-chitosan film coated on the glass carbon electrodes, was developed. For the improvement of the selectivity of artemisinin detection, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-d-glucopyranosyl)-1-O-phenyl]porphyrin (T(o-glu)PPH) metal complex [FeT(o-glu)PPCl] was synthesized and employed as a ARN-sensitive and -selective material in the amperometric sensors. The proposed [FeT(o-glu)PPCl]/Au-nanoparticles modified electrodes showed excellent selectivity and sensitivity toward ARN with respect to a number of interferents and exhibited stable current response, which can be attributed to the coordination of ARN with the [FeT(o-glu)PPCl] in the electrodes. The calibration graph obtained with the proposed sensor was linear over the range of 1.8 × 10⁻⁷-1.7 × 10⁻⁹ mol l⁻¹, with a detection limit of 1.7 × 10⁻⁹ mol l⁻¹ for ARN. Significant advantages of the proposed procedure over the conventional reductive electrochemical methods are the selective detection and the relatively low applied potential requirement of the ARN-sensor. The prepared sensor is applied for the determination of ARN in plant samples and the results agreed with the values obtained by the pharmacopoeia method.     

Kinetics Study on Reaction between Dihydroartemisinic Acid and Singlet Oxygen: An Essential Step to Photochemical Synthesis of Artemisinin

Artemisinin is an excellent antimalarial drug widely used in clinical medicine. However, due to the limitation of natural source of artemisinin, the chemical synthesis of artemisinin has achieved substantial attention. Dihydroartemisinic acid is a key precursor for the synthesis of artemisinin. The reaction of dihydroartemisinic acid with singlet oxygen to form peroxide is a pivotal step in the photochemical preparation of artemisinin. Nevertheless, the reaction kinetics of dihydroartemisinic acid with singlet oxygen has not been investigated previously. Herein, we report the rate constants of the reaction between dihydroartemisinic acid and singlet oxygen. By directly detecting the luminescence decay kinetics of singlet oxygen at 1270 nm at room temperature, the reaction rate constants of singlet oxygen and dihydroartemisinic acid in different solvents are obtained to be 1.81\begin{document}$\times$\end{document}10\begin{document}$^5$\end{document} (mol/L)^-1·s^-1 in CCl\begin{document}$_4$\end{document}, 5.69\begin{document}$\times$\end{document}10\begin{document}$^5$\end{document} (mol/L)^-1·s^-1 in CH\begin{document}$_3$\end{document}CN, and 3.27\begin{document}$\times$\end{document}10\begin{document}$^6$\end{document} (mol/L)^-1·s^-1 in DMSO, respectively. It is found that the reaction rate constants of dihydroartemisinic acid with singlet oxygen increase as polarity of the solvent increases among the three solvents. These results provide fundamental knowledge to optimize experiment conditions of photochemical synthesis of artemisinin for improving the yields of artemisinin.     

高效毛细管电泳电导法测定青蒿素的含量

建立了青蒿中青蒿素含量测定的高效毛细管电泳-电导法,Tris—H3BO3（H3BO3浓度为1．5mmol／L）为电泳介质,乙醇为有机添加剂,在15kV高压,pH9．0的碱性条件下柱端电导法检测了青蒿中的青蒿素含量,着重探讨了缓冲溶液种类、浓度、酸碱度及其操作电压、进样时间对检测的影响。该法的线性范围为20-280mg／L,检出限为3．2mg／L;结果表明该法简便、快速、准确,适用于青蒿素含量的测定。     

正交设计-紫外分光光度法测定青蒿中的青蒿素

以干青蒿叶为原料,考察石油醚萃取青蒿素的工艺条件,如温度、时间、溶剂量及超声功率等因素,正交法确定了最佳萃取工艺条件为温度40℃,超声功率90W,时间20min（两次）,液固比120∶1（mL.g-1）。紫外分光光度法直接测定不同产地青蒿中青蒿素的含量,结果表明：用超声波强化石油醚萃取青蒿素与常规浸泡法石油醚萃取比较,用超声波可以大大缩短萃取时间,提高了萃取率。     

Quantum chemical studies on antimalarial of artemisinin (qinghaosu) derivatives

In this paper theoretical studies were performed on artemisinin (qinghaosu) derivatives with semiempirical quantum chemical methods AMI and PM3. The antimalarial activity -logC has an obvious correlation with the net charge of C(16) and bond orders of bonds O(1)-C(10), O(2)-C(6), O(1)-O(2) and O(5)-C(16). According to the calculation results, we derived structure-activity relationship, presented the probable pharmacophore of qinghaosu derivatives and the interaction fashion between the drugs and the plasmodium receptor.     

Evaluation of the coupling between ultra performance liquid chromatography and evaporative light scattering detector for selected phytochemical applications

Fast analysis in LC can be performed with sub-2 microm particles at very high pressures (up to 1000 bar) known as ultra performance LC (UPLC). With this configuration, it is possible to obtain fast and/or highly efficient separations compared to conventional LC. For the analysis of compounds without chromophores, the evaporative light scattering detector (ELSD) is an attractive alternative because of its quasi-universality, versatility, low-cost and good sensitivity. The UPLC-ELSD was investigated in terms of sensitivity and apparent efficiency, with a conventional ELSD instrument, for two types of commercially available nebulisers, using different mobile phase flow rates and column ids. Results were finally compared with the UPLC-UV configuration. Three applications with phytochemical compounds were selected to highlight the potential of this approach (i.e. the isocratic separations of artemisinin and its derivatives, of calystegines and the gradient separation of several tropane alkaloids). Depending on the used column length, baseline separations were obtained in 3-10 min, with an average apparent efficiency ranging from 7000 to 30,000 plates.     

An amperometric sensor based on hemin adsorbed on silica gel modified with titanium oxide for electrocatalytic reduction and quantification of artemisinin

The present work describes the development of an amperometric sensor based on hemin immobilized on a titanium oxide modified silica toward detection of artemisinin (ARN) in neutral medium at an applied potential of −0.5 V vs. Ag/AgCl. The sensor presented its best performance in 0.1 mol L⁻¹ phosphate buffer solution, at pH 7.0. After optimizing the operational conditions, the sensor provided a linear response range for ARN reduction from 50 nmol L⁻¹ to 1000 nmol L⁻¹ with a sensitivity, detection and quantification limits of 24.66 A L mol⁻¹, 15 nmol L⁻¹ and 52 nmol L⁻¹, respectively. The proposed sensor showed a stable response for at least 80 successive determinations. The repeatability of the measurements with the sensor and the preparation of a series of electrodes, evaluated in terms of relative standard deviation, were 4.1% and 5.0%, respectively, for n = 10. The developed sensor was applied for the determination of ARN in the crude extracts of A. vulgaris L and the average recovery for these samples is 101.4 (± 3.1)%.     

Electrochemical Detection of Artemisinin Using Cobalt Sulphide/Reduced Graphene Oxide Nanocomposite

Solvothermally synthesized cobalt sulphide/reduced graphene oxide (CoS/rGO) was used to fabricate an electrochemical sensor for detection of artemisinin. Microscopic techniques were used to characterize CoS/rGO nanocomposite. The electrochemical sensor was fabricated by modifying the surface of glassy carbon electrode with CoS/rGO nanocomposite. [Fe(CN)6]^3−/4− was used as a mediator to aid oxidation of artemisinin. Differential pulse voltammetric technique was used for the detection of artemisinin. A linear range of 30–100 μM was used. Experimentally, a detection limit of 0.5 μM was obtained. Therefore, the developed sensor can be used for quality control of artemisinin.